Method and device for blank pressing glass bodies

ABSTRACT

The device for blank pressing glass bodies includes a first rotary indexing table with preforms for forming parisons from glass gobs; a second rotary indexing table having pressing molds and pressing tools for pressing the parisons into final form after formation in the preforms; and a device for shifting the first rotary indexing table relative to the second rotary indexing table so that each preform is positionable in a transfer position between a pressing tool and a pressing mold. Each preform is mounted on the first rotary indexing table by a indexable mount for holding it in a first horizontal position or in a second position pivoted away from the first position, so that, when a preform is in the transfer position, the indexable mount can be pivoted, so that a parison in it drops into the pressing mold for pressing by the pressing tool.

The invention relates to a method for producing blank-pressed glass bodies for optical equipment by preforming technology, in which a single molten glass gob is delivered to a levitation preform, and the glass gob, without touching the preform surface, is preformed into a parison which after a defined length of time has elapsed is transferred to a separate pressing mold and is pressed therein into its final form by means of a pressing tool. The invention also relates to a device for performing the method, having two rotary indexing tables, of which one has circularly disposed preforms for making the parisons from a molten glass gob, which preforms have extremely tiny openings in their lower region for introducing an air cushion, and the other has circularly disposed pressing molds for pressing the parisons after transfer from the preforms.

It is known to produce glass bodies for the production of optical equipment, such as lenses, prisms, etc. in highly polished forms, by re-pressing re-warmed, blank (fire-polished) glass rods. The re-pressing is necessary to attain the final precise surface optical quality for the glass bodies. In producing some glass bodies, such as aspherical lenses for automobile headlights, however, the re-pressing operation alone is insufficient. Milling, grinding and polishing operations are necessary in addition. In producing blank-pressed condenser lenses, for instance, only the aspherical surface is blank-pressed, while the plane face opposite the blank face is milled, ground and polished by mechanical operations.

The manual re-pressing and the additional method steps that may be necessary dictate a time-consuming, expensive mode of production. Since there is a very great need for blank-pressed glass bodies, in particular lenses for automobile headlights, the demand for automatic production directly from the molten phase of the glass, that is, after an in-line blank pressing process, arises.

This kind of automatic production is possible by means of the preform technology defined at the outset, which is known for instance from German Patent Disclosure DE-A 24 10 923. The transfer of the glass gob from a preform is effected according to this reference by placing the glass gob on a kind of chute along which the parison is guided in the hot state to a pressing mold. This causes surface defects and changes of shape, which by today are no longer tolerable. The change in shape furthermore leads in the final analysis to an uneven temperature distribution. This too has an adverse effect on shaping in the ensuing pressing operation.

In Japanese Patent Disclosure JP-A 11-157 849, a method of this generic kind has been disclosed. In it, the transfer of the glass gob from a preform is accomplished by opening the preform and causing the glass gob to drop into a pressing mold in free fall. This avoids surface defects and changes of shape. However, there is no way to tell how the interaction of the preform and the pressing mold proceeds.

Against this background, it is now the object of the present invention to refine the generic method such that the transfer of the glass gob from the preform into the pressing mold is performed as effectively as possible. With respect to the device, it is the object of the present invention to refine such a device so that the method can be performed with it.

With respect to the method, this object is attained by the method having the characteristics of claim 1, and with respect to the device, it is attained by a device having the characteristics of claim 5.

In terms of the method, it is proposed that the preform is moved across the pressing mold for transfer of the glass gob, is stopped in this transfer position, and is pivoted downward away from the glass gob. This method can be performed especially favorably, since for this purpose the preform need merely be pivotably connected to a mount. Especially preferably, the pivoting angle is at last 90°.

In a further variant, the preform experiences an acceleration of at least 1 g, that is, the acceleration due to gravity, in executing the pivoting motion. In pictorial terms, the preform must be folded away faster than the glass gob moves along its way in free fall to the pressing mold. As a result, the glass gob reaches the pressing mold without tilting of the preform.

With respect to the device for performing this method, it is provided that the preforms are secured to the aforementioned first rotary indexing table by means of an indexable mount, which keep the preforms horizontally in a first indexing position and which in a second indexing position enable the free fall of the parisons and then maintain position.

An embodiment in which the preforms are pivotably connected to the mounts and can be pivoted downward upon actuation of an actuator is especially preferred. This embodiment makes the variant method possible in which the preforms are pivoted away from the glass gob.

The invention will be described in terms of an example in further detail in conjunction with the drawings. Shown in them are:

FIG. 1: the basic disposition of the two rotary indexing tables of the device;

FIG. 2: the preform in relation to the pressing mold prior to the free fall of the glass gob;

FIG. 3: the disposition of FIG. 2 after the free fall of the glass gob into the pressing mold.

Below, identical reference numerals designate the same elements.

FIG. 1 provides a first overview of the disposition of the various components. Two cooperating rotary indexing tables 6 and 7 can be seen. They are disposed such that they mesh with one another in a transfer position 8. The rotary indexing table 6 has the preforms (not shown) arranged in a circle for forming the parisons. The larger rotary indexing table 7, conversely, has the preforms (not shown) arranged in a circle for pressing the parisons. It can be seen that the rotary indexing table for the pressing molds has more positions than the rotary indexing table 6 for the preforms. This is predominantly due to the fact that each pressing die (not shown) of each pressing tool has its own drive mechanism. This means that the pressing tool can be moved simultaneously while the pressing is stopped. Thus because of the greater complication of the machinery, longer pressing times in proportion to the feeding times are attained.

FIG. 2 now shows the cooperation of the rotary indexing tables 6 and 7. FIG. 2 shows how after a further cycle, the preformer has moved into the region between the pressing tool 3 and the pressing mold 2. The preform 1 is still located in a horizontal position on the indexable mount 4.

After a defined length of time, the actuator 5 of the indexable mount 4 is actuated, specifically in such a way that the preform 1 is moved into the pivoted-away position, as shown in FIG. 3, with an acceleration that is greater than the acceleration due to gravity. The pivoting motion causes the glass gob, or parison (not shown), to fall freely into the pressing mold 2. The pressing mold 2 is then moved upward. In the process, it presses the parison into the final product. 

1-5. (canceled)
 6. A device for blank-pressing glass bodies for optical equipment by preforming technology, said device comprising a first rotary indexing table (6) comprising a plurality of levitation preforms (1) in a circular arrangement thereon, each of said levitation preforms (1) comprising means for preforming a respective molten glass gob delivered thereto into a corresponding parison and having a lower region provided with a plurality of openings for forming an air cushion so that said molten glass gob and said parison formed therefrom do not contact any preform surfaces; a second rotary indexing table (7) comprising a plurality of respective pressing molds (2) and corresponding pressing tools (3) arranged in a circular arrangement thereon, said corresponding pressing tools (3) having drive means for pressing said parisons arranged in said respective pressing molds (2) into a final form after formation and transfer of said parisons to said pressing molds (2); and means for shifting said first rotary indexing table (6) relative to said second rotary indexing table (7) so that each of the preforms (1) is positionable in a transfer position (8) between one of said pressing tools (3) and one of the pressing molds (2) after a predetermined time interval for parison formation; wherein each of the preforms (1) is mounted on the first rotary indexing table (6) by an indexable mount (4) for keeping the respective preform (1) associated with the indexable mount (4) in a first horizontal position for holding parisons or a second position enabling free fall of the parisons, so that, when one of the preforms is in said transfer position, the indexable mount (4) is operated to move said one of the preforms (1) from said first horizontal position into said second position, whereby one of the parisons held in said one of said preforms drops in free fall into said one of said pressing molds for pressing by said one of said pressing tools (3) into said final form.
 7. The device as defined in claim 6, further comprising an actuator (5) for operating said indexable mount (4) to pivot said one of the preforms from said first horizontal position downward and away from said one of said parisons to said second position enabling said free fall of said one of said parisons into said one of said pressing molds.
 8. The device as defined in claim 7, wherein said one of said preforms is pivoted downward from the first horizontal position through an angle of at least 90°.
 9. The device as defined in claim 6 or 7, wherein said one of said preforms (1) experiences an acceleration of at least one g when moved between said first horizontal position and said second position enabling said free fall. 